Plumber fixed a leak in radiator and they are working now but no water coming from hot water taps?

It may well be that when the job was done the plumber (or apprentice) turned off the cold feed to the hot water circuit and forgot to turn it back on. Look under the boiler for isolating valves. There should be two identical. Both should be in line with the pipework (open position). Sometimes they are small taps, sometimes they are slotted for a fat screwdriver. The gas isolator will be colour coded yellow and should not be touched. It won't be trapped air as the mains pressure eliminates air.